How a 13-Ounce Backpack Frame Can Comfortably Carry 150 Pounds

Kuiu relies on aerospace engineering to literally take the weight off your shoulders

Jun 7, 2016
Outside
Outside Magazine
How a 13-Ounce Backpack Frame Can Comfortably Carry 150 Pounds

Corey's wearing Kuiu's Verde camo pattern. As you can see, it's a good fit for this pine forest in northern Idaho. Click to enlarge    Photo: Corey Hass

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Constructed from carbon fiber, Kuiu’s Icon Pro backpack frame weighs just 13 ounces, but is able to comfortably support loads of up to 150 pounds. What gives? Well, by day, I’m actually an aerospace engineer, so I think I can break this down. 

What Is It?

We’ve all seen flashy carbon products, but too often that material is used only to lend stuff a high-tech appearance. Few applications outside of the aerospace industry take full advantage of the strength, rather than just the light weight, of carbon fiber. Available in capacities ranging from 1,850 to 7,200 cubic inches (or 30 to 118 liters), the Icon Pro frame does. It turns the packs into heavy duty load haulers, enabling you to wrestle massive amounts of weight into, and out of, the backcountry. 

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Spot the Corey. Click to enlarge.   Photo: Corey Hass

Who’s It For?

Kuiu targets backcountry hunters with its technically advanced products. The Icon Pro range of packs is specifically designed to carry your back- or bikepacking gear in and your butchered meat out—over long distances, rugged terrain, and through inhospitable weather. But the same merits that enable these packs to comfortably carry an entire deer, or most of an elk, make them equally applicable to wilderness firefighters, mountaineers, outdoor outfitters, or anyone else who needs to schlep a ridiculous amount of equipment around on their backs. We’ve found this pack to work just as well hauling ropes, crampons, shelters, snow anchors, and ice axes to base camp as it does marching meat back to the freezer. 

Design

Let’s get nerdy. Carbon fiber itself is a loose fabric that can come as either single strands (called unidirectional fiber or “uni”) or, more commonly, as a woven fabric made from strands of that uni. A single layer of carbon fiber is exceptionally thin and not at all stiff. But when many layers, or “plys,” are placed on top of each other, with their weaves aligned in specific directions, you get a composite material that's engineered to take loads in specific directions. 

Carbon fiber fabric on its own will not hold any weight, so you must thoroughly coat every single strand of fiber with a resin, usually a liquid that's applied either as the plies are laid or at the material level. When carbon fiber comes with that resin already applied, it’s called “pre-preg.” 

Resins come in many different chemical make-ups, some curing with time alone, while others require heat. Once the resin cures, you are left with the stiff, glossy component we’re all familiar with. It is this gluing together of strands that gives carbon fiber its strength. 

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Laying the carbon fiber plys.   Photo: KUIU

With the help of Rocket Composites, Kuiu took the same principles used for aerospace component design and applied them to a consumer backpack frame. By employing a technique called “wet compression molding,” it's able to rapidly and repeatedly produce parts with minimal risk of human error. Elsewhere, expensive automatic high tonnage presses are required to achieve this method, but cleverly, Rocket and Kuiu use a manual press that can do the same thing at a fraction of the cost. 

Any composite part that is made needs to be placed in a mold to give it a specified shape. Kuiu uses a two-piece mold that controls both sides of the shape, as opposed to more common methods that start with one side and build up from there. Think about lining your cereal bowl with sheets of fabric—that’s the most common way of doing composites and it only controls one surface. If you were able to place another, smaller cereal bowl on the top layer of that fabric and press them together, you can control both top and bottom surfaces. That’s what they’re doing here.  

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The Icon Pro frame in finished form. Side-on (left), and from-the-front (right).   Photo: KUIU

You can see how thin the resulting frame is side-on, and how broad it is, side-to-side. It’s this profile that gives it the vertical strength to transfer so much weight to your hips, from such a big, three-dimensional volume, without flexing. Another clever detail are the small tabs at the frame’s top that interface with the load-stabilization straps. They’ve been reduced in profile, building in a specific degree of flex that enables them to hold a lot of weight, while also flexing with your shoulders, as you move. The end result is the vertical stiffness of a five-pound external aluminum frame, plus the torsional flexibility of a lightweight aluminum wire one. But the thing weighs just 13 ounces! The bottom line: It has the load-hauling ability of an external frame pack with the comfort of a modern, ultralight internal-frame design. 

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Connected to the carbon frame are robust, heavily padded shoulder and hip straps. They're comfortable, up to the pack's capacity.   Photo: KUIU

The frame of a backpack serves to distribute the load across your back, hips, and shoulders so that no single point of your body is carrying all of the load, and to distribute most of that weight onto your hips, where it’s supported by the biggest muscle group in your body: your legs. 

If you asked one of those ultralight packs to haul more than their 30- to 50-pound ratings, their frames would deflect significantly, creating pressure points on your back and pulling down your shoulders. For nearly the same all-up weight, Kuiu packs are able to carry three times as much weight as equivalent ultralight designs. 

kuiu-icon-pro-doe
Hunting helps Idaho manage its large population of whitetail deer, keeping the species within the carrying capacity of the state's environment. It also pays for conservation and management efforts both here, and throughout the country. Hunting is, by far, the single largest economic contributor to conservation there is. Click to enlarge.   Photo: Corey

Using It

This past winter, we set out to chase some white tail deer in the Bitterroot Mountains of northern Idaho. From a base camp, we hiked several miles across rough, mountainous terrain, crossing rivers and stomping through deep snow without the aid of trails. 

On the fourth and final day of the hunt, I was the only one without a deer. Sitting against a fallen tree, and glassing the clearing in front of me, I watched as five doe skirted the edge of the woods before stepping out into the clear cut. That’s when I noticed the antlers on the last one. After taking the shot, we field dressed the deer, quartered it, and de-boned the meat to achieve the lightest possible load. That still left me with 60 pounds of fresh venison to haul out. 

To load the meat bags, you separate the backpack from its frame, then use the compression straps to pull the backpack against the meat, cinching everything together. This way, the heaviest part of your load, the meat, is flush to your back. 

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Corey's been hunting deer for five years. This was the first time he's been successful. Click to enlarge.   Photo: Corey Hass

It was a struggle to swing the pack up to my knee, and pivot into its shoulder straps. But once that hip belt connected, it felt just right. I was extremely surprised at how sturdy the pack felt, and how it doesn’t feel that much different to carry, despite the additional 60 pounds. I couldn’t feel any hotspots or pressure points in the shoulder straps or hip pads. 

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The Icon Pro's rifle sling is another highlight. It kept this Weatherby Mark V Ultra Lightweight out of the way, but instantly accessible. Click to enlarge.   Photo: Corey Hass

Where most other hunting-specific packs integrate a rifle sling that carries the gun vertically, out of your reach, Kuiu has designed a sling that carries the rifle under your arm. This leaves the gun instantly accessible, while keeping it out of harm’s way, and leaving your hands free. With the rifle slung, you can them employ trekking poles to help you safely manage the weight through difficult footing. 

Carrying 80 pounds several miles through the mountains wasn’t easy, but this pack made it as comfortable as possible. 

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Carrying 80 Lbs through terrain like this, without a trail, will never be easy. Massive physical effort like this is one of the untold struggles of hunting. This sport takes real commitment. Click to enlarge.   Photo: Corey Hass

Should You Buy It? 

No pack is perfect for every job, but this thing is dang near close to it. While the frame is exceptionally light, the backpack that hangs on it, and all its straps, are built heavy, to hold up to those heavy loads, and backcountry abuse. Being overbuilt comes at a weight penalty; at 4.25 pounds, the overall pack is light for a hunting pack, but heavier than something designed solely for backpacking. The other penalty: it prioritizes moving your load as close as possible to your back rather than facilitating airflow. You’ll find the ventilation of lightweight packs with mesh suspension to be far greater.

So if you’re simply backpacking with light loads, the Kuiu will be overkill. But if you need to haul 50-plus pounds of gear out of the woods, you won’t find anything better. 

Filed To: Indefinitely Wild

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